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Tribological properties and cutting performance of boron and silicon doped diamond films on Co-cemented tungsten carbide inserts
Diamond & Related Materials 33 (2013) 54–62
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Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond
Tribological properties and cutting performance of boron and silicon doped diamond films on Co-cemented tungsten carbide inserts☆ Liang Wang, Xuelin Lei, Bin Shen, Fanghong Sun ⁎, Zhiming Zhang School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
a r t i c l e
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Article history: Received 31 October 2012 Received in revised form 4 January 2013 Accepted 9 January 2013 Available online 16 January 2013 Keywords: Boron Silicon Doped diamond Tribological Cutting performance
a b s t r a c t Boron and silicon doped diamond films are deposited on the cobalt cemented tungsten carbide (WC-Co) substrate by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Acetone, hydrogen gas, trimethyl borate (C3H9BO3) and tetraethoxysilane (C8H20O4Si) are used as source materials. The tribological properties of boron-doped (B-doped), silicon-doped (Si-doped) diamond films are examined by using a ball-on-plate type rotating tribometer with silicon nitride ceramic as the counterpart in ambient air. To evaluate the cutting performance, comparative cutting tests are conducted using as-received WC-Co, undoped and doped diamond coated inserts, with high silicon aluminum alloy materials as the workpiece. Friction tests suggest that the Si-doped diamond films present the lowest friction coefficient and wear rate among all tested diamond films because of its diamond grain refinement effect. The B-doped diamond films exhibit a larger grain size and a rougher surface but a lower friction coefficient than that of undoped ones. The average friction coefficient of Si-doped, B-doped and undoped diamond films in stable regime is 0.143, 0.193 and 0.233, respectively. The cutting results demonstrate that boron doping can improve the wear resistance of diamond films and the adhesive strength of diamond films to the substrates. Si-doped diamond coated inserts show relatively poor cutting performance than undoped ones due to its thinner film thickness. B-doped and Si-doped diamond films may have tremendous potential for mechanical application. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Depositing chemical vapor deposition (CVD) diamond films on cutting tools have been studied extensively for the extreme hardness and inertness, superior heat conductivity, high wear resistance, low friction and thermal expansion coefficient resistance of CVD diamond films. The tribological and mechanical properties of diamond coated cutting tools can be somewhat affected by the factors such as surface morphology, structure and film thickness. These factors vary with the depositing conditions and substrate treatments. Moreover, the adherence of diamond films to the substrates is important for cutting tools to achieve a long working life [1–7]. The effects caused by incorporation of dopants or impurities such as boron, nitrogen, phosphorous and sulfur in CVD diamond films have been widely investigated. Studies were firstly motivated to realize electronic application by making the CVD diamond conducting. It was found that doping can change the diamond growth behavior and diamond
☆ Originally presented at the International Conference of Diamond and Carbon Materials. ⁎ Corresponding author. Tel.: +86 21 3420 6826. E-mail address: [email protected] (F. Sun). 0925-9635/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.diamond.2013.01.004
structure, while effects of doping on the mechanical properties of diamond films have been less investigated [8–11]. Therefore, it is worth shedding light on the tribological properties and cutting performance of doped diamond films to broaden their application. Boron is one of the most prominent impurities in diamond as boron atoms can be readily incorporated into the diamond lattice and form a p-type semiconductor with tunable electrical conductivity. Boron-doped (B-doped) diamond has been widely researched in electrical and semiconductor materials [12,13]. Referring to tribological properties, Qi Liang et al. [14] studied the tribological properties of boron-doped nanocrystalline diamond deposited on mirror polished Ti-6Al-4V substrates with respect to the relationship between applied normal load (stress) and coefficient of friction. To our knowledge, only a few publications to date describe the effects of silicon addition on the diamond films. Moreover, they mainly focus on the growth and structural characteristics and optoelectronic application of silicon-doped (Si-doped) diamond films [15,16]. Besides, F. Fan et al. prepared a Si incorporated CVD diamond film on co-cemented tungsten carbide (WC-Co) substrate using octamethylcyclotetrasiloxane (D4) as Si precursor. They reveal that Si could be introduced onto the interface between the diamond coatings and the substrates, and thus enhance the coating adhesion [17]. It can be found that the tribological properties and cutting performance of B-doped and Si-doped diamond films on WC-Co substrates are not clear.
L. Wang et al. / Diamond & Related Materials 33 (2013) 54–62
air, and also on the cutting performance in a turning test on an aluminum–silicon alloy material.
Table 1 Deposition parameters of diamond films. Filament temperature Substrate temperature Mixed solution flow rate H2 flow rate Chamber pressure Bias current Duration
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2000–2200 [°C] 800–900 [°C] 80 [sccm] 200 [sccm] 10–35 [Torr] 3 [A] 6 [h]
In this study, we choose a kind of widely investigated doped diamond films and a less investigated one, namely B-doped and Si-doped diamond films, to understand their mechanical properties. We focus on the tribological behaviors of B-doped diamond films and Si-doped diamond films deposited on cemented tungsten carbide inserts in ambient
2. Experiments details 2.1. Substrate pretreatment and film deposition The undoped, B-doped and Si-doped diamond films are deposited by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Flat square shaped WC-6%Co inserts are used as substrate. To enhance the nucleation and to improve the adhesion of diamond films to the substrate, as-received inserts are firstly submitted to react with Murakami's reagent for 30 min and Caro's acid for 1 min, and then abraded with diamond powder. Acetone and hydrogen gas are adopted as source materials. The precursors of boron and silicon are trimethyl borate (C3H9BO3) and
Fig. 1. FESEM micrograph images of the (a,c,e) surface morphology and (b, d, f) cross section of (a, b) undoped (c, d) B-doped and (e, f) Si-doped diamond films deposited on the WC-Co inserts. The insets in (b, d, f) show energy-dispersive X-ray spectrum of the diamond films.
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tetraethoxysilane (C8H20O4Si) respectively, which are dissolved in acetone solution according to preset B/C and Si/C atomic ratio. The mixed solution in the liquid container is introduced in the reactor by part of H2. The flow rate of mixed solution is controlled by the flow rate of carrier gas and the vapor pressure of mixed solution. The vapor pressure of mixed solution is associated with its temperature which is maintained at 0 °C by immersing the container in glacial-aqueous mix solution. The gas phase is activated by 6 electrical heated carburized tantalum wires at intervals of 35 mm, which are 10 mm above the substrate
Fig. 3. Raman spectra of B-doped, Si-doped and undoped diamond films.
surface. The detailed deposition parameters of diamond films are listed in Table 1 [18]. The parameters are set identical, so any change of the tribological and cutting performance of diamond coated inserts is considered to be induced by doping. As-deposited diamond films are characterized by field emission scanning electron microscopy (FESEM), surface profilemeter, X-ray diffraction (XRD) and Raman spectroscopy.
2.2. Friction tests The tribological behaviors of as-fabricated diamond films are evaluated using ball-on-plate type rotating tribometer. Si3N4 ceramic material with the diameter of 6 mm is used as counterpart ball, which is mounted on stationary holder. The planar inserts coated with diamond films are clamped on a rotating table at the angular velocity of 300 RPM. The normal load is constantly 4 N. The contact point is set to be 2 mm eccentric from the center of rotary motion. All tests are conducted in the ambient air with a fixed sliding time of 24 h, corresponding to sliding distances of 5429 m. The wear rate of films and counterpart balls is evaluated by surface profilemeter and optical microscope, respectively. Furthermore, FESEM provided with X-ray Energy Dispersive Spectroscopy (EDS) is used to identify the prevailing wear mechanisms.
Fig. 2. XRD patterns of the undoped, B-doped and Si-doped diamond films.
Fig. 4. Friction coefficient curves (smoothed) of undoped, B-doped and Si-doped diamond films sliding against Si3N4 ceramic ball under ambient air.
L. Wang et al. / Diamond & Related Materials 33 (2013) 54–62
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2.3. Turning tests To evaluate the cutting performance of the three types of diamond films, diamond coated and uncoated WC-Co inserts are used to turning Al-14 wt.% Si alloys. The turning tests are conducted on INDEX G200 turning machine. Cutting parameters are as follows: rotation speed of 2000 r/min; feed of 0.1 mm/r; depth of cut of 0.5 mm. After every cutting pass, the inserts are removed from the tool holder and then cleaned in hydrofluoric (HF) acid to remove adhered Al alloy from the cutting edge. The flank wear is estimated by optical microscopy. FESEM is used to explore the wear mechanism of the inserts.
3. Results and discussion 3.1. Characterization of doped diamond films The morphology and cross-section view of as-deposited diamond films examined by FESEM are compared in Fig. 1. All three types of diamond films exhibit faceted crystallites. Compared to undoped diamond films, B-doped diamond films present a larger grain size, while Si-doped diamond films show rounded clusters and smaller faceted crystallites. The average crystallites size of undoped, B-doped and Si-doped diamond are 1–2 μm, 3–4 μm and 200–500 nm, respectively. Si-doped diamond films display a lower growth rate than that of undoped and B-doped diamond films. The average thickness of coating is about 4 μm, 4.5 μm and 2 μm. The results of energy dispersive X-ray spectrum analysis of diamond films reveal that a small amount of Si was incorporated into the Si-doped diamond coating. Since boron element is a light
Fig. 6. Average friction coefficient in the stable period.
element and/or B peaks may overlap with C peaks, Boron element is not detected in this study. The surface roughness of as-deposited diamond films is measured by surface profilemeter with 5 mm scan length. The arithmetic average (Ra) and the root mean squared (Rq) surface roughness for the Si-doped diamond films with the value of 130.7/177.1 nm are lower than that of undoped (168.2/233.4 nm) and B-doped (206.3/387.9 nm) diamond films. The results indicate that the surface roughness is related to diamond grain size in this study.
Fig. 5. Worn surface of (a) undoped, (b) Si-doped and (c) B-doped diamond films and (d) the EDS analysis of wear debris on B-doped diamond films after frictional test.
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Fig. 7. The optical micrographs of the wear scar and the wear tracks, and corresponding cross-sectional wear profiles of undoped, B-doped and Si-doped diamond films after frictional tests.
The crystalline structure of as-deposited diamond films are detected by XRD with Cu Kα (40 kV/40 mA) radiation source. In the XRD patterns of all samples shown in Fig. 2, peaks at about 43.9° and 75.2° are assigned to (111) and (220) reflections of the diamond, respectively. Undoped and B-doped diamond films also present (311) reflection at about 91.4°, which is absent in the Si-doped diamond films. The results are normalized to diamond (111) peak. The (111) to (220) reflection line peaks ratio I(111)/I(220) of undoped and B-doped and Si-doped diamond films is 1.21, 2.04 and 0.20, respectively. The results suggest that undoped and B-doped diamond films show preferential (111) crystallographic orientation, while Si-doped diamond films tend to grow along the b220 > orientation. The
average lattice constant of undoped, B-doped and Si-doped diamond films are calculated to be 3.5658 Å, 3.5698 Å and 3.5651 Å, respectively. The covalent radius of boron (rB = 0.85 Å) is higher than that of carbon (rC = 0.77 Å), it induces a tensile stress and hence tends to increase the lattice constant of diamond [19]. In the case of Si, the covalent radius of silicon (rSi = 1.11 Å) is much larger than that of carbon, the Si is thus incorporated non-substitutionally with a low solubility. Moreover, Si incorporating may result in a Si-vacancy structure [15]. Therefore, the lattice constant of diamond decreases lightly.
Fig. 8. The wear rate of diamond films and counterpart balls.
Fig. 9. Flank wear of testing inserts as a function of cutting time.
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The chemical quality of as-deposited diamond films is evaluated by Raman spectroscopy using a He–Ne laser with an excitation wavelength of 632.8 nm. The Raman spectra of as-deposited diamond films, which are normalized for 1332 cm −1 band, are shown in Fig. 3. Sharp peak at 1332 cm −1 corresponded to the sp 3 bonding of diamond can be detected from undoped diamond films, indicating the high phase-purity polycrystalline diamond. As for B-doped diamond films, 1332 cm −1 peak changes toward an asymmetric Fanolike lineshape. The broad band around 1000 cm −1 is associated with the Fano effect. The broad bands around 500 cm −1 and 1250 cm −1 may well be associated with the actual boron incorporation in the lattice. Their position agrees with two maxima of the phonon density of states (PDOS) of diamond [20]. Si-doped diamond films present similar quality with undoped diamond films. They also present the first order diamond Raman line at 1332 cm −1, although the line is less sharp than that of undoped ones. The non-diamond carbon or graphite phase generally presents at the grain boundary. Because Si-doped diamond films possess more grain boundary for its smaller crystallites, these broad peaks bands at 1350 cm−1 and 1580 cm−1 corresponding to the sp2 bonded carbon are thus more evident in Si-doped diamond spectrum. This may be due to the fact that the Si-doped diamond films possess smaller crystallites and more grain boundary, where non-diamond carbon or graphite phase is likely located. The shifts of Raman diamond peak to the higher and lower frequency are corresponded to compressive and tensile stresses in the diamond films, respectively. Undoped diamond films and Si-doped diamond films show compressive stress, whereas tensile in-plane biaxial stress can be achieved in B-doped diamond films. The tensile stress is mainly induced by high defect density in the B-doped diamond films and a node-blocked sliding effect at the grain boundary [21].
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The FWHM of 1332 cm −1 for undoped, B-doped and Si-doped diamond films are 9.28, 28.46 and 19.26 cm −1, respectively. The incorporation of the impurity atom of Si in the diamond lattice can cause dilation of the diamond lattice and increases the FWHM of the 1332 cm −1 Raman band [15]. The FWHM increase of B-doped diamond films may be not due to a degradation of the crystalline quality but to the appearance of the Fano effect, which is a complex phonon–electron coupling [22]. 3.2. Friction behaviors The friction coefficient curves of undoped, B-doped and Si-doped diamond films sliding with Si3N4 balls are shown in Fig. 4. The undoped diamond films and Si-doped diamond films undergo a similar friction coefficient evolution. Following the high initial sharp peak, the coefficient of friction (COF) gradually transits to a lower value and finally comes into a steady state. In the case of the B-doped diamond films, the COF also starts with a high value but drops to a low value quickly. An increasing regime then can be observed and eventually the curve presents a relatively steady state. FESEM is used to analyze the wear track. There is no evidence of film delamination and spalling. The wear groove becomes flattened as shown in Fig. 5, revealing the polishing wear mechanism. As the sliding proceeds, the sharp-shaped diamond asperities on the contact interface are gradually worn down and the sliding interface is smoothened. This predominately determines the COF evolution form of undoped and Si-doped diamond films. It's worth noting that a mass of irregularly shaped debris, which is chemically analyzed by EDS integrated with the FESEM, pile up on the wear track of B-doped diamond films. The results of the EDS characterization shown in Fig. 5(d) identify the presence of aluminum, carbon, nitrogen and oxygen elements. Accordingly, we could get the conclusion that the wear debris is materials
Fig. 10. Aluminum adhesion aspect in the (a) uncoated (b) undoped (c) B-doped (d) Si-doped diamond coated tool that machined Al-14 wt.% of silicon after the first cutting pass.
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produced by brittle fracture or adhesive wear of counterpart Si3N4 balls. This means that a fraction of the wear debris may adhere on the sliding interface of B-doped diamond films and balls. At the early stage, the smoothing effect on the sliding interface dominates the friction behavior and thus determines the reducing tendency of friction coefficient presented in the ‘run-in’ period. Afterwards, as the transferred wear debris accumulates, the adhesive strength starts to play predominate role on the friction behavior. Therefore, the friction coefficient stops reducing and presents a slightly rising trend due to the high adhesive strength caused by the interaction between the mating ball surface and the transferred materials. An equilibrium siding interface eventually forms as such rising tendency culminates in a relatively stable state, during which the friction coefficient fluctuates on a steady value [23]. The averaged friction coefficient is obtained by doing statistics on the data collected after sliding 300 min. The mean value and corresponding standard deviation are plotted in Fig. 6. Surprisingly, the stable friction coefficient of B-doped diamond films is lower than that of the undoped diamond films, although the B-doped diamond films present larger crystallites and rougher surface. Two possible explanations are as follows. One is the interaction mechanism between two contacting surfaces being changed because of boron incorporation. The boron carbide chemical bonds may exist in the B-doped diamond films, it would help change the surface frictional energy
dissipation and thus change the COF [14]. The other is that the oxide generated by friction may serve as solid lubrication, which will help to decrease COF for B-doped diamond films. The lowest COF of 0.143 is given by Si-doped diamond films. This may be mainly caused by the smallest diamond crystallites and lowest surface roughness of Si-doped diamond films in all three types of diamond films as the chemical quality of Si-doped diamond films is similar to that of undoped diamond films. The wear rate of counterpart balls and diamond films is also studied. The wear scar is characterized by optical microscopy in magnification of 40 ×. Wear rates of balls are calculated by regarding the wear scar as a circular form. The wear tracks are also observed by optical microscope and the cross-sectional wear profiles are acquired using surface profilemeter. The cross-section wear profiles are then fitted with Gaussian curve to estimate their area. As shown in Fig. 7, the wear track for undoped and B-doped diamond films is quite visible in optical microscopy because of the polishing action. While the wear track of Si-doped diamond films is relatively shallow and not distinct as others. The wear rates of diamond films are determined by the wear volume loss divide by normal load and total sliding distance. The calculated wear rates are plotted in Fig. 8. The ball sliding with Si-doped diamond films gives the lowest wear rate, followed by balls sliding with B-doped diamond films and undoped diamond films. The measured
Fig. 11. Images of flank wear of uncoated inserts after turning for (a) 38 s, (b) 114 s, (d) 152 s and (d) 190 s; Si-doped diamond coated inserts after turning for (e) 38 s, (f) 76 s, (g) 114 s and (h) 190 s; undoped diamond coated inserts after turning for (i) 38 s, (j) 114 s, (k) 190 s and (l) 266 s; B-doped diamond coated inserts after turning for (m) 38 s, (n) 190 s, (o) 380 s and (p) 912 s.
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wear rate of Si-doped diamond films with 6.96E-9 mm3/Nm is lower by two orders of magnitude than that of undoped diamond films. The results suggest that a low wear rate of counterpart balls and diamond films can be obtained for those films whose COF is low.
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3.3. Cutting performance The flank wear of all examined inserts as a function of cutting time is compared in Fig. 9. According to ISO 3685, flank wear of 0.3 mm is employed as the tool failure criterion. However, to clarify the failure mechanism, we proceed the cutting process even if the flank wear exceeds 0.3 mm. As illustrated, the flank wear of uncoated inserts shows a rapid increase and reaches 0.5 mm only after one turning pass of 38 s. The Si-doped diamond coated inserts also show an insufficient wear resistant as they give 0.29 mm of flank wear after turning for 38 s. Undoped diamond coated inserts show 0.52 mm wear width after machining for 266 s. B-doped diamond coated inserts give a steady increasing of flank wear. After turning for 900 s, the flank wear is only 0.42 mm. The life of undoped and B-doped diamond coated insert is 150 s and 380 s, respectively. The images of aluminum adhesion on the flank face of inserts are shown in Fig. 10. The uncoated inserts present severe aluminum adhesion compared with diamond coated inserts, whether they are undoped, B-doped or Si-doped diamond coated inserts. A small quantity of adhesion of aluminum alloy also can be detected on the coated inserts, while it just situates in the worn area where the WC-Co substrate is exposed. The low adhesion of aluminum for diamond coated inserts can be attributed to the excellent tribological performance of diamond films. The images of worn inserts etched by HF acid after different cutting pass of the tests are illustrated in Fig. 11. It can be found that diamond films gradually wear down and expose the WC-Co substrate, which can be further confirmed by the FESEM micrograph as depicted in Fig. 12. During the cutting process, although there are no diamond films on the wear area, no large areas of delamination of all three types of diamond films can be detected, thus the inserts are worn gradually. The typical wear pattern of flank wear shown in Fig. 11 is also a strong proof of the gradual wear behavior. We supposed that Si-doped diamond coated inserts could show a good cutting performance because Si-doped diamond films show an excellent tribological property in sliding tests. Disappointedly, Si-doped diamond coated insert failed quickly. During the cutting process, the aluminum alloys adhere to and peel off the flank face alternately. Furthermore, it can be clearly noted that the notch forms on the wear pattern of uncoated and Si-doped diamond coated inserts. The notch reveals the abrasive action of hard silicon particles in the soft aluminum matrix [2]. The relatively thin Si-doped diamond films, which are revealed in Fig. 1, cannot withstand the combined effects of adhesive and abrasive wear. Consequently, high flank wear and low working life can be achieved by Si-doped diamond coated inserts, much less the uncoated ones. Fig. 12 suggests some differences in the junction of the diamond films and WC-Co substrate. The B-doped diamond films present a sloping wear surface while the undoped and Si-doped diamond films show a vertical fracture plane. This may be ascribed to the adhesive strength of B-doped diamond films to the substrate that is higher than that of undoped diamond and Si-doped diamond films. The relatively high wear resistance of B-doped diamond films and adhesive strength guarantee that the B-doped diamond coated inserts can withstand the co-impact of abrasive and adhesive wear of workpiece. 4. Conclusions
Fig. 12. FESEM micrograph of (a) undoped, (b) B-doped and (c) Si-doped diamond coated inserts after turning tests.
Boron-doped (B-doped) and silicon-doped (Si-doped) diamond films are deposited on chemically treated WC-6%Co inserts by using bias-enhanced HFCVD method. Silicon doping can refine the crystalline size but reduce the growth rate. The results of Raman spectra indicate that the B-doped diamond films present tensile stress while undoped and Si-doped diamond films show compressive stress. The friction tests show that the B-doped diamond films presented lower friction coefficient, when sliding with Si3N4 ceramic materials,
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compared to undoped diamond films although B-doped diamond films have relatively larger grain size and rougher surface. There is more Si3N4 ceramic debris in the frictional interface of B-doped diamond films and counterpart than that of undoped and Si-doped diamond films. The adhered transferred materials make the transition regime in the friction coefficient evolution of B-doped diamond films differs from that of undoped and Si-doped diamond films. After the initial high peak, the curve of B-doped diamond films first drops to a low value and then increases to some degree before transiting to the steady state. While for undoped and Si-doped diamond films, the coefficient directly transits to the steady state. The Si-doped diamond films display excellent tribological property. They present the lowest wear rate of the films and the counterpart ball, followed by B-doped diamond and undoped diamond films. The flank wear of uncoated inserts, which is mainly induced by adhesive and abrasive wear, surpasses the failure criterion in one cutting pass when turning Al–Si alloy materials. B-doped diamond coated inserts exhibit excellent cutting performance due to the high wear resistance and adhesive strength to the substrate of B-doped diamond films. They provide lowest flank wear and thus longest working life than the other testing inserts. However, Si-doped diamond coated inserts have no-advantage for cutting Al–Si alloy materials in this study, which could be due to the thinner film thickness obtained in the same depositing time compared with undoped and B-doped diamond coated inserts.
Prime novelty statement This study examined the tribological properties of boron-doped and silicon-doped diamond films deposited on cemented tungsten carbide inserts in the ambient air, and also the cutting performances in a turning test on an aluminum–silicon alloy material. The results could broaden the utilization of boron-doped and silicon-doped diamond films into the mechanical and tribological applications.
Acknowledgments This research is sponsored by the National Natural Science Foundation of China (no. 50975177, no. 51005154), the Chenguang Program of Shanghai Municipal Education Commission (no. 12CG11) and the Tribology Science Fund of State Key Laboratory of Tribology. References [1] H. Yoshikawa, A. Nishiyama, Diam. Relat. Mater. 8 (1999) 1527–1530. [2] P. Roy, S.K. Sarangi, A. Ghosh, A.K. Chattopadhyay, Int. J. Refract. Met. Hard Mater. 27 (2009) 535–544. [3] E. Uhlmann, W. Reimers, F. Byrne, M. Klaus, Prod. Eng. 4 (2010) 203–209. [4] F.H. Sun, Z.M. Zhang, M. Chen, H.S. Shen, Diam. Relat. Mater. 12 (2003) 711–718. [5] D.C. Zhang, B. Shen, F.H. Sun, Appl. Surf. Sci. 256 (2010) 2479–2489. [6] S.K. Sarangi, A. Chattopadhyay, A.K. Chattopadhyay, Appl. Surf. Sci. 254 (2008) 3721–3733. [7] D.G. Bhat, D.G. Johnson, A.P. Malshe, H. Naseem, W.D. Brown, L.W. Schaper, C.H. Shen, Diam. Relat. Mater. 4 (1995) 921–929. [8] R. Haubner, S. Bohr, B. Lux, Diam. Relat. Mater. 8 (1999) 171–178. [9] M. Werner, R. Locher, Rep. Prog. Phys. 61 (1998) 1665–1710. [10] R. Haubner, Diam. Relat. Mater. 14 (2005) 355–363. [11] W. Kalss, S. Bohr, R. Haubner, B. Lux, M. Griesser, H. Spicka, M. Grasserbauer, P. Wurzinger, Int. J. Refract. Met. Hard Mater. 14 (1996) 137–144. [12] R.J. Zhang, S.T. Lee, Y.W. Lam, Diam. Relat. Mater. 5 (1996) 1288–1294. [13] Z.L. Wang, C. Lu, J.J. Li, C.Z. Gu, Appl. Surf. Sci. 255 (2009) 9522–9525. [14] Q. Liang, A. Stanishevsky, Y.K. Vohra, Thin Solid Films 517 (2008) 800–804. [15] D.V. Musale, S.R. Sainkar, S.T. Kshirsagar, Diam. Relat. Mater. 11 (2002) 75–86. [16] S. Orlanducci, V. Sessa, E. Tamburri, M.L. Terranova, M. Rossi, S. Botti, Surf. Coat. Technol. 201 (2007) 9389–9394. [17] F. Fan, W. Tang, S. Liu, L. Hei, C. Li, G. Chen, F. Lu, Surf. Coat. Technol. 200 (2006) 6727–6732. [18] B. Shen, F.H. Sun, Diam. Relat. Mater. 18 (2009) 238–243. [19] M. Roy, A.K. Dua, J. Nuwad, K.G. Girija, A.K. Tyagi, S.K. Kulshreshtha, J. Appl. Phys. 100 (2006). [20] P.W. May, W.J. Ludlow, M. Hannaway, P.J. Heard, J.A. Smith, K.N. Rosser, Chem. Phys. Lett. 446 (2007) 103–108. [21] W.L. Wang, M.C. Polo, G. Sanchez, J. Cifre, J. Esteve, J. Appl. Phys. 80 (1996) 1846–1850. [22] C. Lévy-Clément, in: Akira Fujishima, Yasuaki Einaga, Tate Narasinga Rao, Donald A. Tryk (Eds.), Diamond Electrochemistry, Elsevier B.V, Amsterdam, 2005, pp. 80–114. [23] B. Shen, F.H. Sun, Chin. J. Mech. Eng. 22 (2009) 658–664.
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Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond
Tribological properties and cutting performance of boron and silicon doped diamond films on Co-cemented tungsten carbide inserts☆ Liang Wang, Xuelin Lei, Bin Shen, Fanghong Sun ⁎, Zhiming Zhang School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
a r t i c l e
i n f o
Article history: Received 31 October 2012 Received in revised form 4 January 2013 Accepted 9 January 2013 Available online 16 January 2013 Keywords: Boron Silicon Doped diamond Tribological Cutting performance
a b s t r a c t Boron and silicon doped diamond films are deposited on the cobalt cemented tungsten carbide (WC-Co) substrate by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Acetone, hydrogen gas, trimethyl borate (C3H9BO3) and tetraethoxysilane (C8H20O4Si) are used as source materials. The tribological properties of boron-doped (B-doped), silicon-doped (Si-doped) diamond films are examined by using a ball-on-plate type rotating tribometer with silicon nitride ceramic as the counterpart in ambient air. To evaluate the cutting performance, comparative cutting tests are conducted using as-received WC-Co, undoped and doped diamond coated inserts, with high silicon aluminum alloy materials as the workpiece. Friction tests suggest that the Si-doped diamond films present the lowest friction coefficient and wear rate among all tested diamond films because of its diamond grain refinement effect. The B-doped diamond films exhibit a larger grain size and a rougher surface but a lower friction coefficient than that of undoped ones. The average friction coefficient of Si-doped, B-doped and undoped diamond films in stable regime is 0.143, 0.193 and 0.233, respectively. The cutting results demonstrate that boron doping can improve the wear resistance of diamond films and the adhesive strength of diamond films to the substrates. Si-doped diamond coated inserts show relatively poor cutting performance than undoped ones due to its thinner film thickness. B-doped and Si-doped diamond films may have tremendous potential for mechanical application. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Depositing chemical vapor deposition (CVD) diamond films on cutting tools have been studied extensively for the extreme hardness and inertness, superior heat conductivity, high wear resistance, low friction and thermal expansion coefficient resistance of CVD diamond films. The tribological and mechanical properties of diamond coated cutting tools can be somewhat affected by the factors such as surface morphology, structure and film thickness. These factors vary with the depositing conditions and substrate treatments. Moreover, the adherence of diamond films to the substrates is important for cutting tools to achieve a long working life [1–7]. The effects caused by incorporation of dopants or impurities such as boron, nitrogen, phosphorous and sulfur in CVD diamond films have been widely investigated. Studies were firstly motivated to realize electronic application by making the CVD diamond conducting. It was found that doping can change the diamond growth behavior and diamond
☆ Originally presented at the International Conference of Diamond and Carbon Materials. ⁎ Corresponding author. Tel.: +86 21 3420 6826. E-mail address: [email protected] (F. Sun). 0925-9635/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.diamond.2013.01.004
structure, while effects of doping on the mechanical properties of diamond films have been less investigated [8–11]. Therefore, it is worth shedding light on the tribological properties and cutting performance of doped diamond films to broaden their application. Boron is one of the most prominent impurities in diamond as boron atoms can be readily incorporated into the diamond lattice and form a p-type semiconductor with tunable electrical conductivity. Boron-doped (B-doped) diamond has been widely researched in electrical and semiconductor materials [12,13]. Referring to tribological properties, Qi Liang et al. [14] studied the tribological properties of boron-doped nanocrystalline diamond deposited on mirror polished Ti-6Al-4V substrates with respect to the relationship between applied normal load (stress) and coefficient of friction. To our knowledge, only a few publications to date describe the effects of silicon addition on the diamond films. Moreover, they mainly focus on the growth and structural characteristics and optoelectronic application of silicon-doped (Si-doped) diamond films [15,16]. Besides, F. Fan et al. prepared a Si incorporated CVD diamond film on co-cemented tungsten carbide (WC-Co) substrate using octamethylcyclotetrasiloxane (D4) as Si precursor. They reveal that Si could be introduced onto the interface between the diamond coatings and the substrates, and thus enhance the coating adhesion [17]. It can be found that the tribological properties and cutting performance of B-doped and Si-doped diamond films on WC-Co substrates are not clear.
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air, and also on the cutting performance in a turning test on an aluminum–silicon alloy material.
Table 1 Deposition parameters of diamond films. Filament temperature Substrate temperature Mixed solution flow rate H2 flow rate Chamber pressure Bias current Duration
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2000–2200 [°C] 800–900 [°C] 80 [sccm] 200 [sccm] 10–35 [Torr] 3 [A] 6 [h]
In this study, we choose a kind of widely investigated doped diamond films and a less investigated one, namely B-doped and Si-doped diamond films, to understand their mechanical properties. We focus on the tribological behaviors of B-doped diamond films and Si-doped diamond films deposited on cemented tungsten carbide inserts in ambient
2. Experiments details 2.1. Substrate pretreatment and film deposition The undoped, B-doped and Si-doped diamond films are deposited by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Flat square shaped WC-6%Co inserts are used as substrate. To enhance the nucleation and to improve the adhesion of diamond films to the substrate, as-received inserts are firstly submitted to react with Murakami's reagent for 30 min and Caro's acid for 1 min, and then abraded with diamond powder. Acetone and hydrogen gas are adopted as source materials. The precursors of boron and silicon are trimethyl borate (C3H9BO3) and
Fig. 1. FESEM micrograph images of the (a,c,e) surface morphology and (b, d, f) cross section of (a, b) undoped (c, d) B-doped and (e, f) Si-doped diamond films deposited on the WC-Co inserts. The insets in (b, d, f) show energy-dispersive X-ray spectrum of the diamond films.
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tetraethoxysilane (C8H20O4Si) respectively, which are dissolved in acetone solution according to preset B/C and Si/C atomic ratio. The mixed solution in the liquid container is introduced in the reactor by part of H2. The flow rate of mixed solution is controlled by the flow rate of carrier gas and the vapor pressure of mixed solution. The vapor pressure of mixed solution is associated with its temperature which is maintained at 0 °C by immersing the container in glacial-aqueous mix solution. The gas phase is activated by 6 electrical heated carburized tantalum wires at intervals of 35 mm, which are 10 mm above the substrate
Fig. 3. Raman spectra of B-doped, Si-doped and undoped diamond films.
surface. The detailed deposition parameters of diamond films are listed in Table 1 [18]. The parameters are set identical, so any change of the tribological and cutting performance of diamond coated inserts is considered to be induced by doping. As-deposited diamond films are characterized by field emission scanning electron microscopy (FESEM), surface profilemeter, X-ray diffraction (XRD) and Raman spectroscopy.
2.2. Friction tests The tribological behaviors of as-fabricated diamond films are evaluated using ball-on-plate type rotating tribometer. Si3N4 ceramic material with the diameter of 6 mm is used as counterpart ball, which is mounted on stationary holder. The planar inserts coated with diamond films are clamped on a rotating table at the angular velocity of 300 RPM. The normal load is constantly 4 N. The contact point is set to be 2 mm eccentric from the center of rotary motion. All tests are conducted in the ambient air with a fixed sliding time of 24 h, corresponding to sliding distances of 5429 m. The wear rate of films and counterpart balls is evaluated by surface profilemeter and optical microscope, respectively. Furthermore, FESEM provided with X-ray Energy Dispersive Spectroscopy (EDS) is used to identify the prevailing wear mechanisms.
Fig. 2. XRD patterns of the undoped, B-doped and Si-doped diamond films.
Fig. 4. Friction coefficient curves (smoothed) of undoped, B-doped and Si-doped diamond films sliding against Si3N4 ceramic ball under ambient air.
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2.3. Turning tests To evaluate the cutting performance of the three types of diamond films, diamond coated and uncoated WC-Co inserts are used to turning Al-14 wt.% Si alloys. The turning tests are conducted on INDEX G200 turning machine. Cutting parameters are as follows: rotation speed of 2000 r/min; feed of 0.1 mm/r; depth of cut of 0.5 mm. After every cutting pass, the inserts are removed from the tool holder and then cleaned in hydrofluoric (HF) acid to remove adhered Al alloy from the cutting edge. The flank wear is estimated by optical microscopy. FESEM is used to explore the wear mechanism of the inserts.
3. Results and discussion 3.1. Characterization of doped diamond films The morphology and cross-section view of as-deposited diamond films examined by FESEM are compared in Fig. 1. All three types of diamond films exhibit faceted crystallites. Compared to undoped diamond films, B-doped diamond films present a larger grain size, while Si-doped diamond films show rounded clusters and smaller faceted crystallites. The average crystallites size of undoped, B-doped and Si-doped diamond are 1–2 μm, 3–4 μm and 200–500 nm, respectively. Si-doped diamond films display a lower growth rate than that of undoped and B-doped diamond films. The average thickness of coating is about 4 μm, 4.5 μm and 2 μm. The results of energy dispersive X-ray spectrum analysis of diamond films reveal that a small amount of Si was incorporated into the Si-doped diamond coating. Since boron element is a light
Fig. 6. Average friction coefficient in the stable period.
element and/or B peaks may overlap with C peaks, Boron element is not detected in this study. The surface roughness of as-deposited diamond films is measured by surface profilemeter with 5 mm scan length. The arithmetic average (Ra) and the root mean squared (Rq) surface roughness for the Si-doped diamond films with the value of 130.7/177.1 nm are lower than that of undoped (168.2/233.4 nm) and B-doped (206.3/387.9 nm) diamond films. The results indicate that the surface roughness is related to diamond grain size in this study.
Fig. 5. Worn surface of (a) undoped, (b) Si-doped and (c) B-doped diamond films and (d) the EDS analysis of wear debris on B-doped diamond films after frictional test.
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Fig. 7. The optical micrographs of the wear scar and the wear tracks, and corresponding cross-sectional wear profiles of undoped, B-doped and Si-doped diamond films after frictional tests.
The crystalline structure of as-deposited diamond films are detected by XRD with Cu Kα (40 kV/40 mA) radiation source. In the XRD patterns of all samples shown in Fig. 2, peaks at about 43.9° and 75.2° are assigned to (111) and (220) reflections of the diamond, respectively. Undoped and B-doped diamond films also present (311) reflection at about 91.4°, which is absent in the Si-doped diamond films. The results are normalized to diamond (111) peak. The (111) to (220) reflection line peaks ratio I(111)/I(220) of undoped and B-doped and Si-doped diamond films is 1.21, 2.04 and 0.20, respectively. The results suggest that undoped and B-doped diamond films show preferential (111) crystallographic orientation, while Si-doped diamond films tend to grow along the b220 > orientation. The
average lattice constant of undoped, B-doped and Si-doped diamond films are calculated to be 3.5658 Å, 3.5698 Å and 3.5651 Å, respectively. The covalent radius of boron (rB = 0.85 Å) is higher than that of carbon (rC = 0.77 Å), it induces a tensile stress and hence tends to increase the lattice constant of diamond [19]. In the case of Si, the covalent radius of silicon (rSi = 1.11 Å) is much larger than that of carbon, the Si is thus incorporated non-substitutionally with a low solubility. Moreover, Si incorporating may result in a Si-vacancy structure [15]. Therefore, the lattice constant of diamond decreases lightly.
Fig. 8. The wear rate of diamond films and counterpart balls.
Fig. 9. Flank wear of testing inserts as a function of cutting time.
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The chemical quality of as-deposited diamond films is evaluated by Raman spectroscopy using a He–Ne laser with an excitation wavelength of 632.8 nm. The Raman spectra of as-deposited diamond films, which are normalized for 1332 cm −1 band, are shown in Fig. 3. Sharp peak at 1332 cm −1 corresponded to the sp 3 bonding of diamond can be detected from undoped diamond films, indicating the high phase-purity polycrystalline diamond. As for B-doped diamond films, 1332 cm −1 peak changes toward an asymmetric Fanolike lineshape. The broad band around 1000 cm −1 is associated with the Fano effect. The broad bands around 500 cm −1 and 1250 cm −1 may well be associated with the actual boron incorporation in the lattice. Their position agrees with two maxima of the phonon density of states (PDOS) of diamond [20]. Si-doped diamond films present similar quality with undoped diamond films. They also present the first order diamond Raman line at 1332 cm −1, although the line is less sharp than that of undoped ones. The non-diamond carbon or graphite phase generally presents at the grain boundary. Because Si-doped diamond films possess more grain boundary for its smaller crystallites, these broad peaks bands at 1350 cm−1 and 1580 cm−1 corresponding to the sp2 bonded carbon are thus more evident in Si-doped diamond spectrum. This may be due to the fact that the Si-doped diamond films possess smaller crystallites and more grain boundary, where non-diamond carbon or graphite phase is likely located. The shifts of Raman diamond peak to the higher and lower frequency are corresponded to compressive and tensile stresses in the diamond films, respectively. Undoped diamond films and Si-doped diamond films show compressive stress, whereas tensile in-plane biaxial stress can be achieved in B-doped diamond films. The tensile stress is mainly induced by high defect density in the B-doped diamond films and a node-blocked sliding effect at the grain boundary [21].
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The FWHM of 1332 cm −1 for undoped, B-doped and Si-doped diamond films are 9.28, 28.46 and 19.26 cm −1, respectively. The incorporation of the impurity atom of Si in the diamond lattice can cause dilation of the diamond lattice and increases the FWHM of the 1332 cm −1 Raman band [15]. The FWHM increase of B-doped diamond films may be not due to a degradation of the crystalline quality but to the appearance of the Fano effect, which is a complex phonon–electron coupling [22]. 3.2. Friction behaviors The friction coefficient curves of undoped, B-doped and Si-doped diamond films sliding with Si3N4 balls are shown in Fig. 4. The undoped diamond films and Si-doped diamond films undergo a similar friction coefficient evolution. Following the high initial sharp peak, the coefficient of friction (COF) gradually transits to a lower value and finally comes into a steady state. In the case of the B-doped diamond films, the COF also starts with a high value but drops to a low value quickly. An increasing regime then can be observed and eventually the curve presents a relatively steady state. FESEM is used to analyze the wear track. There is no evidence of film delamination and spalling. The wear groove becomes flattened as shown in Fig. 5, revealing the polishing wear mechanism. As the sliding proceeds, the sharp-shaped diamond asperities on the contact interface are gradually worn down and the sliding interface is smoothened. This predominately determines the COF evolution form of undoped and Si-doped diamond films. It's worth noting that a mass of irregularly shaped debris, which is chemically analyzed by EDS integrated with the FESEM, pile up on the wear track of B-doped diamond films. The results of the EDS characterization shown in Fig. 5(d) identify the presence of aluminum, carbon, nitrogen and oxygen elements. Accordingly, we could get the conclusion that the wear debris is materials
Fig. 10. Aluminum adhesion aspect in the (a) uncoated (b) undoped (c) B-doped (d) Si-doped diamond coated tool that machined Al-14 wt.% of silicon after the first cutting pass.
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produced by brittle fracture or adhesive wear of counterpart Si3N4 balls. This means that a fraction of the wear debris may adhere on the sliding interface of B-doped diamond films and balls. At the early stage, the smoothing effect on the sliding interface dominates the friction behavior and thus determines the reducing tendency of friction coefficient presented in the ‘run-in’ period. Afterwards, as the transferred wear debris accumulates, the adhesive strength starts to play predominate role on the friction behavior. Therefore, the friction coefficient stops reducing and presents a slightly rising trend due to the high adhesive strength caused by the interaction between the mating ball surface and the transferred materials. An equilibrium siding interface eventually forms as such rising tendency culminates in a relatively stable state, during which the friction coefficient fluctuates on a steady value [23]. The averaged friction coefficient is obtained by doing statistics on the data collected after sliding 300 min. The mean value and corresponding standard deviation are plotted in Fig. 6. Surprisingly, the stable friction coefficient of B-doped diamond films is lower than that of the undoped diamond films, although the B-doped diamond films present larger crystallites and rougher surface. Two possible explanations are as follows. One is the interaction mechanism between two contacting surfaces being changed because of boron incorporation. The boron carbide chemical bonds may exist in the B-doped diamond films, it would help change the surface frictional energy
dissipation and thus change the COF [14]. The other is that the oxide generated by friction may serve as solid lubrication, which will help to decrease COF for B-doped diamond films. The lowest COF of 0.143 is given by Si-doped diamond films. This may be mainly caused by the smallest diamond crystallites and lowest surface roughness of Si-doped diamond films in all three types of diamond films as the chemical quality of Si-doped diamond films is similar to that of undoped diamond films. The wear rate of counterpart balls and diamond films is also studied. The wear scar is characterized by optical microscopy in magnification of 40 ×. Wear rates of balls are calculated by regarding the wear scar as a circular form. The wear tracks are also observed by optical microscope and the cross-sectional wear profiles are acquired using surface profilemeter. The cross-section wear profiles are then fitted with Gaussian curve to estimate their area. As shown in Fig. 7, the wear track for undoped and B-doped diamond films is quite visible in optical microscopy because of the polishing action. While the wear track of Si-doped diamond films is relatively shallow and not distinct as others. The wear rates of diamond films are determined by the wear volume loss divide by normal load and total sliding distance. The calculated wear rates are plotted in Fig. 8. The ball sliding with Si-doped diamond films gives the lowest wear rate, followed by balls sliding with B-doped diamond films and undoped diamond films. The measured
Fig. 11. Images of flank wear of uncoated inserts after turning for (a) 38 s, (b) 114 s, (d) 152 s and (d) 190 s; Si-doped diamond coated inserts after turning for (e) 38 s, (f) 76 s, (g) 114 s and (h) 190 s; undoped diamond coated inserts after turning for (i) 38 s, (j) 114 s, (k) 190 s and (l) 266 s; B-doped diamond coated inserts after turning for (m) 38 s, (n) 190 s, (o) 380 s and (p) 912 s.
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wear rate of Si-doped diamond films with 6.96E-9 mm3/Nm is lower by two orders of magnitude than that of undoped diamond films. The results suggest that a low wear rate of counterpart balls and diamond films can be obtained for those films whose COF is low.
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3.3. Cutting performance The flank wear of all examined inserts as a function of cutting time is compared in Fig. 9. According to ISO 3685, flank wear of 0.3 mm is employed as the tool failure criterion. However, to clarify the failure mechanism, we proceed the cutting process even if the flank wear exceeds 0.3 mm. As illustrated, the flank wear of uncoated inserts shows a rapid increase and reaches 0.5 mm only after one turning pass of 38 s. The Si-doped diamond coated inserts also show an insufficient wear resistant as they give 0.29 mm of flank wear after turning for 38 s. Undoped diamond coated inserts show 0.52 mm wear width after machining for 266 s. B-doped diamond coated inserts give a steady increasing of flank wear. After turning for 900 s, the flank wear is only 0.42 mm. The life of undoped and B-doped diamond coated insert is 150 s and 380 s, respectively. The images of aluminum adhesion on the flank face of inserts are shown in Fig. 10. The uncoated inserts present severe aluminum adhesion compared with diamond coated inserts, whether they are undoped, B-doped or Si-doped diamond coated inserts. A small quantity of adhesion of aluminum alloy also can be detected on the coated inserts, while it just situates in the worn area where the WC-Co substrate is exposed. The low adhesion of aluminum for diamond coated inserts can be attributed to the excellent tribological performance of diamond films. The images of worn inserts etched by HF acid after different cutting pass of the tests are illustrated in Fig. 11. It can be found that diamond films gradually wear down and expose the WC-Co substrate, which can be further confirmed by the FESEM micrograph as depicted in Fig. 12. During the cutting process, although there are no diamond films on the wear area, no large areas of delamination of all three types of diamond films can be detected, thus the inserts are worn gradually. The typical wear pattern of flank wear shown in Fig. 11 is also a strong proof of the gradual wear behavior. We supposed that Si-doped diamond coated inserts could show a good cutting performance because Si-doped diamond films show an excellent tribological property in sliding tests. Disappointedly, Si-doped diamond coated insert failed quickly. During the cutting process, the aluminum alloys adhere to and peel off the flank face alternately. Furthermore, it can be clearly noted that the notch forms on the wear pattern of uncoated and Si-doped diamond coated inserts. The notch reveals the abrasive action of hard silicon particles in the soft aluminum matrix [2]. The relatively thin Si-doped diamond films, which are revealed in Fig. 1, cannot withstand the combined effects of adhesive and abrasive wear. Consequently, high flank wear and low working life can be achieved by Si-doped diamond coated inserts, much less the uncoated ones. Fig. 12 suggests some differences in the junction of the diamond films and WC-Co substrate. The B-doped diamond films present a sloping wear surface while the undoped and Si-doped diamond films show a vertical fracture plane. This may be ascribed to the adhesive strength of B-doped diamond films to the substrate that is higher than that of undoped diamond and Si-doped diamond films. The relatively high wear resistance of B-doped diamond films and adhesive strength guarantee that the B-doped diamond coated inserts can withstand the co-impact of abrasive and adhesive wear of workpiece. 4. Conclusions
Fig. 12. FESEM micrograph of (a) undoped, (b) B-doped and (c) Si-doped diamond coated inserts after turning tests.
Boron-doped (B-doped) and silicon-doped (Si-doped) diamond films are deposited on chemically treated WC-6%Co inserts by using bias-enhanced HFCVD method. Silicon doping can refine the crystalline size but reduce the growth rate. The results of Raman spectra indicate that the B-doped diamond films present tensile stress while undoped and Si-doped diamond films show compressive stress. The friction tests show that the B-doped diamond films presented lower friction coefficient, when sliding with Si3N4 ceramic materials,
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compared to undoped diamond films although B-doped diamond films have relatively larger grain size and rougher surface. There is more Si3N4 ceramic debris in the frictional interface of B-doped diamond films and counterpart than that of undoped and Si-doped diamond films. The adhered transferred materials make the transition regime in the friction coefficient evolution of B-doped diamond films differs from that of undoped and Si-doped diamond films. After the initial high peak, the curve of B-doped diamond films first drops to a low value and then increases to some degree before transiting to the steady state. While for undoped and Si-doped diamond films, the coefficient directly transits to the steady state. The Si-doped diamond films display excellent tribological property. They present the lowest wear rate of the films and the counterpart ball, followed by B-doped diamond and undoped diamond films. The flank wear of uncoated inserts, which is mainly induced by adhesive and abrasive wear, surpasses the failure criterion in one cutting pass when turning Al–Si alloy materials. B-doped diamond coated inserts exhibit excellent cutting performance due to the high wear resistance and adhesive strength to the substrate of B-doped diamond films. They provide lowest flank wear and thus longest working life than the other testing inserts. However, Si-doped diamond coated inserts have no-advantage for cutting Al–Si alloy materials in this study, which could be due to the thinner film thickness obtained in the same depositing time compared with undoped and B-doped diamond coated inserts.
Prime novelty statement This study examined the tribological properties of boron-doped and silicon-doped diamond films deposited on cemented tungsten carbide inserts in the ambient air, and also the cutting performances in a turning test on an aluminum–silicon alloy material. The results could broaden the utilization of boron-doped and silicon-doped diamond films into the mechanical and tribological applications.
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